Generation Rate of Carbon Monoxide from CO₂ Arc Welding

Abstract

Objectives: CO poisoning has been a serious industrial hazard in Japanese workplaces. Although incomplete combustion is the major cause of CO generation, there is a risk of CO poisoning during some welding operations. The aim of the present study was to evaluate the generation rate of CO from CO₂ arc welding under controlled laboratory conditions and estimate the ventilation requirements for the prevention of CO poisoning. Methods: Bead on plate welding was carried out with an automatic welding robot on a rolled steel base metal under several conditions. The concentration of emitted CO from the welding was measured by a real-time CO monitor in a well-ventilated laboratory that was free from ambient CO contamination. The generation rate of CO was obtained from the three measurements–the flow rate of the welding exhaust gas, CO concentration in the exhaust gas and the arcing time. Then the ventilation requirement to prevent CO poisoning was calculated. Results: The generation rate of CO was found to be 386–883 ml/min with a solid wire and 331–1,293 ml/min with a flux cored wire respectively. It was found that the CO concentration in a room would be maintained theoretically below the OSHA PEL (50 ppm) providing the ventilation rate in the room was 6.6–25.9 m³/min. The actual ventilation requirement was then estimated to be 6.6–259 m³/min considering incomplete mixing. Conclusions: In order to prevent CO poisoning, some countermeasures against gaseous emission as well as welding fumes should be taken eagerly.